This invention relates to a moldable silicone rubber sponge composition, to silicone rubber sponge, and to a method for producing silicone rubber sponge.
Silicone rubber sponge, by virtue of its excellent resistance to heat and weathering and its light weight, is used for automotive components such as packings, gaskets, and O-rings; as a surface covering for the rolls used in copiers; and for a variety of sealing materials. A large number of moldable silicone rubber sponge compositions have already been disclosed. For example, Japanese Published Patent Application Sho 44-461 (461/1969) and Japanese Laid Open Patent Application Hei 7-247436 (247,436/1995) teach moldable silicone rubber sponge compositions that contain a thermally decomposable blowing agent as typified by azobisisobutyronitrile. Japanese Laid Open Patent Application Number Hei 10-36544 (36,544/1998) teaches a composition comprising hollow thermoplastic silicone resin particles blended into a liquid silicone rubber composition that evolves gas during its cure. In the case of the former two compositions, however, the decomposition products produced by the thermally decomposable blowing agent during foaming are harmful to humans and thus are problematic from the standpoint of environmental pollution. The silicone rubber sponge produced by the composition taught in Japanese Laid Open Patent Application Number Hei 10-36544 has a poor mechanical strength and hence suffers from limitations in its applications.
The inventors achieved the present invention as the result of investigations directed to solving the problems described above. More specifically, the object of this invention is to provide a moldable silicone rubber sponge composition that during foaming does not generate gas harmful to humans and that curcs to give a silicone rubber sponge that has uniform and microfine cells and a high mechanical strength.